Cable derate for equipment lugs, such as CB's

Isaiah

Senior Member
The January 2018 CEC, Section 4 "Conductors" (Ref Figure 4-3 and Table 4-3) allows a conductor ‘splice’ from 90Deg C to 75Deg C cable for the last 1.2M ‘free-air’ length with conductors separated at the first , incoming connector, which apparently allows (according to table 4-3) use of the 90Deg C temp rating for cable ampacity. First of all is this interpretation correct?
Second, does anyone out there know if this also allowed in the US NEC?
thanks in advance.
 
Yes it is correct. The termination temperature only applies to the first 1.2 meters of conductor connected to equipment. The rest of the conductor can be rated at its temperature rating.
 

kwired

Electron manager
The January 2018 CEC, Section 4 "Conductors" (Ref Figure 4-3 and Table 4-3) allows a conductor ‘splice’ from 90Deg C to 75Deg C cable for the last 1.2M ‘free-air’ length with conductors separated at the first , incoming connector, which apparently allows (according to table 4-3) use of the 90Deg C temp rating for cable ampacity. First of all is this interpretation correct?
Second, does anyone out there know if this also allowed in the US NEC?
thanks in advance.
Yes. NEC requires termination on the CB to be at 60/75C (whichever applies) ampacity but for ampacity adjustment reasons you still can start adjustments from 90 C ampacity if you have 90C conductors.

Also you can transition from 60/75C to 90C via a 90C rated splicing device and even go back to 60/75C at other end of run with another 90C splicing device. NEC doesn't specify any length of conductor that I am aware of that would be the equivalent to your mentioned 1.2M 'free air' length.
 

Isaiah

Senior Member
Yes. NEC requires termination on the CB to be at 60/75C (whichever applies) ampacity but for ampacity adjustment reasons you still can start adjustments from 90 C ampacity if you have 90C conductors.

Also you can transition from 60/75C to 90C via a 90C rated splicing device and even go back to 60/75C at other end of run with another 90C splicing device. NEC doesn't specify any length of conductor that I am aware of that would be the equivalent to your mentioned 1.2M 'free air' length.
Thanks Kwired, but my understanding is according to NEC even if you perform the action you've described above, you nonetheless have to use the 60/75C degree columns at the term's/lugs, i.e. you can derate for ampacity at the middle of the run using 90 Deg C, but not at the ends. The CEC is a little different; as long as you dont exceed 4 feet after you 'break-out' from the 3/C cable you can land using the single conductors at the lugs using 90Dec C.
 

kwired

Electron manager
Thanks Kwired, but my understanding is according to NEC even if you perform the action you've described above, you nonetheless have to use the 60/75C degree columns at the term's/lugs, i.e. you can derate for ampacity at the middle of the run using 90 Deg C, but not at the ends. The CEC is a little different; as long as you dont exceed 4 feet after you 'break-out' from the 3/C cable you can land using the single conductors at the lugs using 90Dec C.
Are you saying they allow you to use conductor at 90C ampacity if cable sheath is removed, for up to four feet from the breaker?

NEC does not allow that. It would allow you to run (does not give any length, but breakers do sink some heat into conductors so that has to have some consideration) 60/75C conductor to a splice rated for 90C then run 90C conductor sized per 90C ampacity table. Depending on termination at other end, may need to use another 90C splicing method and then another 60/75C conductor to your supplied equipment again.
 

Isaiah

Senior Member
Are you saying they allow you to use conductor at 90C ampacity if cable sheath is removed, for up to four feet from the breaker?

Thats my understanding, but with the NEC you're always restricted to the temp at the lugs.

NEC 90 deg.C insulation allows you to derate for ambient corrections, number of conductors in raceway, and underground burial. But, the final step is to compare the result with the 75deg. (or 60deg.C) column, the lower of the two values cannot be exceeded.
 

david luchini

Moderator
Staff member
Thats my understanding, but with the NEC you're always restricted to the temp at the lugs.

NEC 90 deg.C insulation allows you to derate for ambient corrections, number of conductors in raceway, and underground burial. But, the final step is to compare the result with the 75deg. (or 60deg.C) column, the lower of the two values cannot be exceeded.
Kwired is suggesting using the 90deg ampacity between two 90deg rated lugs. That would be NEC compliant.
 
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